


My Demon

by ArsenicHazard



Category: The Infernal Devices Series - Cassandra Clare
Genre: Ascension, Blood, Character Death, Demons, Drugs, Fights, Grief/Mourning, M/M, Pain, Parabatai, Parabatai Bond, Parabatai Feels, Transformation, Yin Fen, heronstairs
Language: English
Status: Completed
Published: 2020-02-08
Updated: 2020-02-08
Packaged: 2021-02-27 18:29:07
Rating: Not Rated
Warnings: Major Character Death
Chapters: 6
Words: 3,092
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/22620262
Author URL: https://archiveofourown.org/users/ArsenicHazard/pseuds/ArsenicHazard
Summary: Jem had always known that he was dying, but this time, he doesn't exactly stay dead.
Relationships: Jem Carstairs/Will Herondale
Comments: 1
Kudos: 20





	1. Chapter 1

Will had noticed Jem had changed from the very beginning. His hair had been beyond silver, if that was even such a thing, and he had acted differently. It was very minor at first. Jem was less patient with him, he would go for the kill strike during practice, only to just barely stop. Then he would smile. As if just playing around. Small things. It had only increased from there, but Will didn’t mention it. Not because he was scared, no, but Jem had been more active, more involved and Will enjoyed that.   


It was when Jem talked to him about death blatantly, was Will starting to worry.   


“It’s hardly scary anymore, Will.” He had said one night when they had stayed up, in the library. Will had closed his book, glancing over at him.   


“..But it’s your life.” He said “You still need to be there. Remember our promise?”   


Jem had merely shrugged at that, as if the thought of breaking their ‘you stay living and I will too’ promise was something in the wind.   


Jem’s skin had begun to look more ashy recently. When Will asked about it, clearly concerned for his friend, Jem had said outright that he was taking more yin fen.   


“I feel fine, William. I feel  _ better _ like this.”   


“But it’s killing you faster!” He had retorted, raising his voice higher than he probably should have. Jem had just shaken his head, but the next few days didn’t seem to change.   


A month had passed like this, Will struggling not to bring it up with his parabatai, but he could feel it. Like a deep-set worry in his bones. Jem was dying faster than before. Exponentially even. He just hoped he would be alright, even though that was a very slim chance.   


Months had passed before something had seriously gone wrong. Will woke up to Jem moaning in pain. He had taken up sleeping in the armchair in Jem’s room recently, finding excuses to stay. Rushing over to his friend’s side, he checked his temperature. The coughing fit started just moments after, and Will grabbed a handkerchief, dabbing at the bits of blood. Looking down at the silvery eyes, he sighed, kissing his head. “Deep breath, love. I’m right here.” He promised. The coughing had stopped, Jem’s eyes closing only for an immense pain to rip through Will. He fought the urge to cry out as he clutched his arm.   


Pulling back his sleeve, to his horror, their shared rune had begun to bleed.    


“No.. nonononono!” He said in a rush, clutching onto Jem, shaking him slightly. “Stay with me!”   


His skin still felt slightly warm, but when the rune decreased in colour to a pale white, Will finally broke down. Charlotte had rushed in at some time, Will hadn’t noticed as he clung to his parabatai.   


“..Come back to me… You promised..” He sobbed, holding onto the lifeless body. Pain ripped through him, hearing Charlotte’s voice, trying to urge him to let go, but he didn’t do anything of the sort.  He buried his face in Jem’s clothes, shoulders shaking with each unstable breath.   


“Jem..” He whispered hoarsely. “..I love you…”


	2. Chapter 2

About three months had passed since Jem had departed to the next life. They had held a funeral, but Will hadn’t truly been the same. He rarely spoke, slept in his brother’s room most nights, only to wake up sobbing and clutching the pillow. He refused most missions, and most people in the Institute didn’t protest his absence. He was left to grieve, rarely finding enough energy to do much else.    


He hadn’t packed up any of Jem’s things, not wanting to move them. On the odd occasion, the head of the Institute would find him broken down, clutching the violin tightly, but when she had asked if he wished to confide in someone, he would say he was fine and turn the offer down.   


Jem would know that he wasn’t fine. Jem always knew exactly what Will was thinking or feeling.    


At the beginning, of course, everyone had worried, especially when he had refused to eat or interact. Eventually, he began showing up to dinner, making a few comments here and there when asked directly, but nothing else.   


Time had passed like this, days melding together for Will. Without Jem, everything seemed so… utterly pointless. Which is exactly why he never brought up that he was beginning to regularly feel pains to anyone.   


It had gotten to the point of unbearable when he had finally gone to Charlotte.   


“I don’t understand it, William.” She had said, looking over at him, the firm expression softening when he had come to her for help. “I’ve never heard of someone feeling like this. It’s not grief… Maybe we should call the Silent Brothers.”   


Will had agreed on the grounds that he would find out what it is and how to fix it.   


Silent Brothers always gave him an uneasy feeling, but this time, when they arrived, it had seemed like almost a relief. They, of all people, would know what was wrong with him. However, they didn’t seem to follow the same agreement that Charlotte had promised, ushering Charlotte into her office for a private ‘talk’. She had come out rather pale, looking over at Will as if he was some mystical creature.   


“Will you tell what it is, Charlotte?” Will had inquired once the Brothers had departed.   


She looked over at him, sighing slowly, having avoided answering him beforehand. “Will, even the Brothers can’t figure it out. The best guess they have is… impossible.”   


“Try me.” He said, folding his arms quietly.   


“They say you have… symptoms of an ascension.”   


Will had only heard the term a few times in his life, some of those times from old books. When someone  _ became _ a divine being. Obviously it wouldn’t be him. Of all people, he was most likely the least holy.   


As Charlotte explained it, it seemed that the angelic power within his blood was consuming the mundane part. That’s why it was so painful.    


Jem would have made some sort of calm joke about Will secretly being the holiest person in the room, despite his actions. Will would have countered with an example of how that was beyond ridiculous.  He was not angelic… and yet, here he was, being told he was somehow becoming more and more  _ angel _ every day.   


With this new information in mind, Charlotte had kept an extra close watch over Will and his behavior. Will felt no different, but slowly, it became more and more real, and less like some strange fantasy.  He could almost sense it. It wasn’t until the true, fiery burn within him that he believed it. Like wings sprouting from his back; like the mundane part of him being destroyed.   


Then he believed it. 


	3. Chapter 3

A year after Jem’s death, and although the grief was still palpable, this new version of himself seemed to handle it better. He was calmer. Felt more confident in himself, rather than just cocky. He was the same old Will… but stronger –physically, as well.   


It was the exact date of Jem’s death when he would be really put to the test. He slept lightly, typically because now he did not need to sleep. It was... a mundane thing he no longer required. Like eating, which he also still continued to do.   


The door to Jem’s room had opened, him lying awake in the bed, staring at the ceiling. He sat up quietly, looking over as the figure crossed the threshold.   


“Will?” It was Charlotte’s voice. He got out of bed, standing and moving over to her.    


“What’s the matter, Charlotte?”   


“I think you should hear about this… There was an attack. On a mundane home not far from here. The eldest daughter of the family was killed.”   


His breath caught in his throat slightly as he nodded for her to go on. Her voice quieted, almost nervous, which was a trait Charlotte rarely possessed. “Her blood was used to write on the wall… ‘William’.”   


This was meant for him, and they both knew it. However, who would want to taunt him like this? Who would specifically call on him, blatantly asking for a fight?   


Only a select group of people knew about the pseudo-curse that he had believed as a young boy.   


“I will go immediately, Charlotte. Thank you for telling me.” He was doing his best to contain his anger. Someone was taunting him. Holding his past over his head, and he was ready to teach them a lesson. Grabbing his gear, Charlotte held his arm before he left, making him stop.    


“Be safe, Will.”   


He gave her a consoling sort of smile in return. “Of course I will. What would you possibly do without me around here?” He joked gently. It drew a smile out of her, which was satisfying enough for him as he turned, his boots making little noise as he moved down the stairs to the front entrance. He headed out, using the direction Charlotte had given him to find the home.    


The house itself looked quaint. It was far enough into the night that the lack of lights was understandable. Any passerby would have just assumed that they were all asleep. But he knew better than that. Heading up the walkway, he pushed open the door, the wood splintered by the hinges, left ajar.   


Moving down the darkened corridor, he found the library, opening the door, knife at the ready. Looking around, he noticed the word, written on the wall. Looking at it for a moment, he took a small breath. 

“Long time no see, William.”   


His eyes widened, blood turning to ice at the voice one he could never forget.


	4. Chapter 4

Will turned quietly, almost not believing his eyes as the smiling figure walked towards him.   


“I figured it would be easier to meet this way.”   


“..You’re… no.”   


The figure gave a soft, calm chuckle. “Yes. I am.”   


He wanted to just rush over to the silver haired figure. To embrace him, and never let go. But this situation set him on edge.   


“Jem… You died.” As if to prove it to himself, he touched the faded rune on his arm.   


“Technically yes, I did. But all based on relativity, on the contrary I could say the same for you.” James stepped closer, the grin never leaving his face. “I can sense it, you know. The human, the mundane part of you is gone William. You’ve been... taken over. As have I, only, now it seems we are truly opposites. Seems familiar to those Holy Stories we read as children, hm?”   


“Cain and Abel.” Will said quietly, looking at him. That would mean that Jem was-   


“Yes, William, do keep up. A demon.” The smirk turned darker. Jem always knew what he was thinking.   


“How?” Was all the dark haired boy could say.   


“Much like you and your angelic power, the yin fen took over my body. When I died, it kept me alive. My soul is gone. I am finally free of all those  _ feelings _ .”    


Will shook his head. “Free? James, what about us? What about Charlotte and Jessamine and...everyone back at the institute? What about me?” He moved closer to him, wanting to reach out and touch him; wanted to hold him in his arms once again. Jem’s skin was even more pale, his teeth appearing almost jagged, and with a closer look, Will could confirm that they were. Easy enough to rip apart flesh with ease. And his eyes: the gorgeous silver that he had grown to love gazing into was now filled with black. There were no whites, only a pit darkness.   


Before he could even touch him, he was receiving a sharp kick in the gut. He stumbled slightly back, coughing a little as he glanced up at him.   


“So terribly sorry, William,” Jem replied, sarcasm that Will had never heard before laced in his voice. “But unlike you, I’m no longer weak. I no longer have to care.” He smiled. “And it feels  _ glorious. _ Now come on and fight me. Let’s end this once and for all. Let’s find out which side would truly win.”   


The dark haired boy stared at him, straightening. Both of them drew their blades, but Will shook his head, chucking his to the ground with a clatter.   


“No. I’m not hurting you.”   


Jem laughed. A dark, sadistic laugh. “Always so sentimental, Herondale.” Grabbing Will by the front of his shirt, he threw him into a bookshelf like it was nothing. He supposed Jem was also stronger. The bookcase wobbled as he caught his footing, righting himself and shaking his head.   


“You don’t have to do this, James. You can still redeem yourself…” Once more receiving a sharp blow to the face, he felt his nose bleed slightly.   


“Pick up your sword and fight me, Will! Stop trying to play the hero! It will get you nowhere.” Jem growled. Raising an arm, he chucked the knife in his hand, hitting Will’s shoulder as the other boy grimaced. In quick succession, Jem was advancing on him, kicking out his knees as he collapsed to the ground, holding up no resistance.   


Jem crouched, grabbing his curls, lifting his face to look into the dark blue eyes. “Fight me, William.”   


“No.” Came the short reply, much to the demon’s aggravation. Kicking into his ribs, he turned, walking away. Will coughed, pulling himself up from the ground, looking at the other’s back.   


“I love you, James. I will not hurt you. You may destroy me, tear me limb from limb, ruin me. I will never do anything that would hurt you. This isn’t the James I know. I know you’re in there… somewhere. Come back to me, Jem.”   


The silver haired boy scoffed, shaking his head. “That person is long gone. And good riddance.”   


Will moved slowly over to him, taking hold of his shoulder. The flinch he felt gave him hope. Jem may know him better than anyone else, but he knew Jem like they were one in the same.   


“Jem…” He started.   


“NO!” Whirling around, Jem hit him hard in the jaw. He could taste blood, spitting it out and looking at the other, who was fuming by now. “Stop with this nonsense, brother!”   


Of all the things in the world, it was these words that got him to smile. “..You called me brother.” He pulled him into a tight hug, grinning happily. That was of course, until he felt the knife pierce his abdomen, driven in with a brutal force.   


“Sentimental.”


	5. Chapter 5

Will’s eyes widened as he pulled back, looking down at the knife in his stomach, clutching at the blood that was slowly running from the wound. He glanced back at Jem, taking a slow breath.   


“Jem…” He stared at the other who just stood there. He couldn’t read the expression as his parabatai watched, finding a bookshelf to support his weight.   


Holding the wound, he shook his head, forcing a smile onto his face. “It’s alright. I understand.” He managed, his voice hoarse.   


Jem shook his head. He had expected the tactic to feel liberating, but all he could feel was a pain inside himself. He hesitated, watching the blood leak through his shirt, over his hands and onto the floor.  Stepping forward a bit, he reached out, slowly pressing a hand to the wound. Will grimaced, but didn’t say anything more.    


“No…” Jem whispered. This was all wrong. This feeling of… worry. Of fear for Will. It all became too clear that he did not want Will to die. “No wait. Make it stop…”   


Slowly easing the other to the ground, he examined the wound, biting his upper lip. “..Just hold still William.” He said quietly. Will could only smile. His Jem. That’s who he saw again.   


The bleeding was slowly ceasing, Will’s angelic powers making the process speed up beyond human abilities.   


“I love you James.”   


The other boy looked back at him, this time putting on a smile.   


“…I know.”   



	6. Chapter 6

When Jem had stayed with him that night, he had known that things would never be the same again. After agreeing to go through the process of humanizing him, the demon and Will undertook extensive experiments to return him back to the same old Jem.   


It was not pleasant for either of them, Jem strapped to a chair, most days screaming for it to end while Will profusely apologized, injecting him with his own angelic blood. He only hoped that Jem would not hate him for it afterwards. It took several weeks before there were signs of improvement. Jem’s eyes had returned to their normal colour –a dark brown that was natural, unlike the soulless black or the yin fen silver. His hair was beginning to darken and each injection was less and less painful.   


Will would sit up throughout the night, watching him sleep, smiling faintly. His Jem was back.   


After another week or so, Will brought Jem back to the Institute. He was Nephilim again, able to cross over the threshold by way of Will’s blood in his system.   


“Finally home, brother.” Will commented.   


Jem looked over at him, nodding and giving a calm smile. “Finally. I don’t know about you, but I am exhausted.”   


Will nodded in agreement. The loss of blood had taken its toll, and unknowing to Jem, he had been taking small amounts of Jem’s blood, which, in these small doses, was not enough to do serious damage, but enough to balance out the angelic blood.   


“Let’s go rest then. I’m sure nobody would refuse us a bit of sleep before dinner. I’m famished.”   


Taking Jem’s hand, he walked up the stairs to the boy’s room, both of them flopping onto the bed with a couple shared grins.   


Pulling his arms around the thinner boy, Will let out a breath, relieved to hear his breathing once more.   


“I’d say that was quite the adventure. Agreed that we should stick to much more mundane problems?” Jem suggested.   


“Like battling against the bloodthirsty waterfowl in Hyde Park?”   


“Yes, Will, just like that.”   


“Then, agreed.”    


The boys laughed, Will taking the opportunity to nuzzle into the other, humming as he yawned. Jem’s breath had evened out, almost asleep.   


“Jem?”   


“Hm?” Came the soft response.   


“I love you.”   


The smile that formed on the other’s face was of relief as he opened his eyes, gazing into the sapphire blue ones that were staring back.   


“I love you too, William.”


End file.
